There are numerous types of drive assemblies for photographic printers. One such drive assembly is described in Johnson, U.S. patent application Ser. No. 08/931,570 entitled "Print Head Drive Assembly" of which is a commonly owned co-pending Patent Application. Johnson discloses a print head that is driven by a motor, gear train, and associated wire such that the print head moves one line at a time over the stationary film unit.
In particular, to accomplish the advancement of the print head in Johnson, a worm gear is attached to the motor. The worm gear has worm gear teeth which are spaced such that an integral number, N of rotations of the worm gear corresponds to the distance between consecutive lines of the image, where N can be any integer greater than zero including one.
In mechanical communication with the worm gear is a drive gear. The drive gear is also in mechanical communication with the print head such that movement of the drive gear causes linear motion of the print head. The drive gear has drive gear teeth which interdigitate with the worm gear teeth such that rotation of the worm gear moves the print head by the predetermined amount, which, in turn, moves the print head by the distance between consecutive lines in the image.
The Johnson print head drive assembly advances a print head having static or rigid properties and thus is not susceptible to physical changes or deformations (such as twisting or bending) while it is advanced/driven/transported. While the print head drive assembly of Johnson is entirely satisfactory from a performance standpoint for driving a print head, it does not address the issues of driving a film medium as in the present invention.
Being that a film unit is flexible (compared to the prior art print head), there arises a need in the art for an effective system to drive the film unit past a stationary print head whereby the film unit can be accurately monitored and tracked for any changes or hesitations while it is advanced/driven.
Furthermore, the Johnson print head assembly would not be suited for a portable printing system as in the present invention. The relatively heavy weight of a print head (as opposed to a film unit) makes the print head more susceptible to shock, vibration, and gravitational orientation.
There arises a need in the art for accurately exposing advancing film in a portable printing system that is not susceptible to shock, vibration, and gravitational orientation.
Moreover, with regard to the Johnson print head assembly the transversal of the print head over the stationary film unit requires larger system volume than the present invention.
There arises a need in the art for accurately exposing advancing film in a portable printing system wherein the print head occupies minimal system volume.
Finally, the Johnson Print head assembly requires two motors (spread roller motor and drive gear motor), as opposed to only one motor of the present invention. The additional motor requires extra components and system volume as compared with the present invention. There arises a need in the art for accurately exposing advancing film in a printing system that minimizes the number of components so as to minimize system volume requirements and manufacturing costs.
It is stated in Takimoto, U.S. Pat. No. 5,032,911 entitled "Video Image Printer Using Liquid Crystal Light Valves and Primary Auxiliary Direction Scanning", and herein incorporated by reference, that a printer is coupled to a video camera wherein the film is exposed successively line by line, and is introduced between the squeezing rollers in synchronism with exposure of the film. The Takimoto patent further states that the squeezing rollers serve as a means for spreading processing solutions, and pressing the film there between, while at the same time feeding the film in the auxiliary scanning direction. The Takimoto patent fails to disclose how the feed or scan is accomplished so as to avoid defects in the film's exposure.
A primary concern of the present invention film unit drive assembly is providing an accurate system of advancing or driving the film unit while the print head emits consecutive lines of the image data for exposing the film unit.
In particular, the print head is stationery while the film unit is advanced proximately thereto. Once the initial lines on the leading side of the film unit have been exposed then the processing fluid spread system begins to spread the processing fluid in a thin layer between the sheet elements, while the trailing portion of the film unit continues to be exposed. Since the advancing film unit is simultaneously exposed and processed, the processing fluid spread system may affect how smoothly the film unit is advanced. The ability for the film unit to be advanced at a relatively constant rate may be detrimentally affected by the forces created by the processing fluid spread system.
Also, since the present invention involves driving a film unit that has a flexible medium (unlike a rigid print head of the prior art), the film unit is vulnerable to being bent, twisted, or altered as it is advanced through the processing fluid spread system and the film unit drive assembly.
It also should be noted that the processing fluid spread system will need to restrict the liquid wave front, caused by the ruptured container (pod), from encroaching on the line of exposure provided by the stationary print head on the advancing film unit. Thus, the permitted shape and extent (down stream) of the wave front for the fluid processing aspect is significantly less than for the allowable wave front of the prior art.
There is therefore a need in the art for an effective method of driving the film unit so that it may be simultaneously exposed with high accuracy by a stationary print head and processed uniformly by the processing fluid spread system.
In particular, a need remains for a film unit drive assembly which can minimize the mechanical errors and the film medium deformations and interferences or hesitations imparted by the drive assembly system itself, as well as imparted by the fluid processing spread system. Also, the need arises to be able to monitor the position of the advancing film unit in light of any residual mechanical errors and the film media deformations and interferences that may still persist.